Pebble

Gravel (from Middle High German kis = coarse gritty sand) is a particle size designation and widespread unconsolidated sediment or a loose ground floor.

• 2.1 Understanding
• 2.2 Usage and Properties
• 2.3 Characteristics

Geoscience definitions

In the geological sense is the designation for a gravel for a grain size and on the other for an unconsolidated sediment.

Gravel as grain size

The grain size of gravel covers according to DIN 4022 rounded rock or mineral grains having a grain diameter between 2 mm and 63 mm, which are coarser than coarse sand. Here, the following grain size fractions are distinguished according to DIN 4022 in a sediment or sedimentary rock by the equivalent diameter:

For the grain sizes medium gravel and coarse gravel and pebbles, the term is used colloquially.

Gravel as unconsolidated sediment

Loosening the sediment is called gravel or crushed when it is more than 50 % of the components of the gravel particle size or greater. These components are generally referred to as detritus. Gravel is a typical sediment of rivers with steep gradients. The transport in streams and rivers is done as floor or towing cargo, ultimately, provides with adequate transport distance for the Zurundung the grains. Loose sediments with predominantly non-rounded or sharp-edged components are called debris.

The deposited at a glacier front in the form of an end moraine typical mixture of rounded edges rock fragments and finer-grained material, summarized under the term total sediment also contains cobbles. A laterally ( ie within a deposit horizon laterally offset ) increasing proportion of rubble indicates the transition from pure glacial to glazifluvialen deposits, ie deposits of meltwater.

Gravels and gravel can solidify in the course of geologic time, when dissolved in water minerals in the sediment fill in the gaps ( cementation ). A certain degree of consolidation is also produced by compaction, ie under pressure as a result of superimposition by other layers of rock. Of such consolidated gravels and gravel are called conglomerates. In predominantly round or sharp-edged components, so-called fragments, the term breccia is used instead conglomerate.

Due to the large average grain Diameter gravel has a large pore volume, making it an excellent aquifer.

Technical context

Basic

In civil engineering or geotechnical sense gravel is a loose rock bottom, which is defined according to the DIN 18196 and DIN EN ISO 14668-1 exclusively on the grain size. Gravel in the technical sense, different particle shapes (eg, round, sharp-edged ), which caused either by natural processes or produced artificially (eg crushers ). The further breakdown in fine, medium and coarse gravel is the same as in the geosciences ( see above).

Use and characteristics

Gravel for the construction industry is an important raw material dar. He finds there use as aggregate ( aggregate ) in concrete, as fill material in earthworks. Due to its high pore volume and high water permeability associated (permeability) is pure gravel is also suitable as a filter layer for drainage in wet ground. In addition, medium and coarse gravel are used because of their well-suited for pore size than burnishing ( capillary breaking layer) below foundation beds to prevent a rise of ground moisture. Since pure gravel contains no plant nutrients and surface water can seep rapidly, it is only sparsely covered by vegetation (eg Magerrasen ).

The promotion of the construction material gravel, the sand is next to the main mass of raw material, done in gravel surface mines or gravel pits. The obtained there, usually inhomogeneous mixtures of different grain sizes are washed and separated into treatment plants. For special purposes will a finer sieves. For applications in construction and winter services edged minerals such as crushed by crushers are sometimes also made of gravel.

Characteristics

• Bulk density: 1.44 to 1.6 t / m³ ( dry)
• Specific heat capacity: 0.84 kJ / kg · K